Scan Input Vs file output resolution

[alanmcd]

At Luminous-Landscape, the ratio on page 12
http://luminous-landscape.com/wp-con...nner-Final.pdf
is given as: 6400ppi scan of 6x7cm negative gives a printable 58x40in
So if all I want is to get 30x20 prints from a 4x5 negative, 1800ppi scans would provide an almost 1 for 1 ratio of input to digital file output ready for printing.
Am I understanding this correctly?
He is assuming a 360ppi printing. My service is asking asking for 254ppi file. I know I don't want to upsample (ie. invent pixels) but is there a problem with 'downsampling' or is there less issue with this. It doesn't have to be an exact one for one does it?

Also: The Luminous paper talks about outputting at 16bit/channel mode. But my printer is asking for 8bit/channel. What is the effect of doing this? The file size of half but does this reduce the quality of the print ?

Thanks
Alan

[alen]

Output 2 versions of the image, then do a test print print and find out exactly. Yes you will burn ink and paper but you will know exactly what you will get.

[RHITMrB]

There is no issue with downsampling, and in fact, depending on your workflow, it may be better to downsample. Photoshop's default downsampling algorithm produces sharpening as a side effect - in Photoshop you can choose "Bicubic" instead of "Automatic" or "Bicubic Sharper" if the added sharpening bothers you.

[Jeff T]

Scan at 16bit if your image needs heavy adjustments in Photoshop. Edit the 16bit file Photoshop, save a copy as 16bit file, reduce to 8bit and save a final copy for printing.

If you're scanning 4x5 films then 8bit is sufficient for printing in most cases.

[onnect17]

Alan,
Allow me to make a couple of suggestions.

Try to scan at closest native resolution of the scanner.
254 x 30" = 7620
7620 / 5" = 1524
So the closest resolution above should be 2400 dpi, if using an Epson.

PS is not my first choice for interpolation work. Search for "QImage" or "Perfect Resize". Both do a decent job.
Double check the proportions. 20x30 will require some cropping in the 4x5.
Ask the printer for the preferred profile and convert the final image to it before reducing the file to 8 bits.

Good luck.

[alanmcd]

Scan at 16bit if your image needs heavy adjustments in Photoshop. Edit the 16bit file Photoshop, save a copy as 16bit file, reduce to 8bit and save a final copy for printing.

If you're scanning 4x5 films then 8bit is sufficient for printing in most cases.

Good point - thank you.
Alan

[alanmcd]

Alan,
Allow me to make a couple of suggestions.

Try to scan at closest native resolution of the scanner.
254 x 30" = 7620
7620 / 5" = 1524
So the closest resolution above should be 2400 dpi, if using an Epson.

PS is not my first choice for interpolation work. Search for "QImage" or "Perfect Resize". Both do a decent job.
Double check the proportions. 20x30 will require some cropping in the 4x5.
Ask the printer for the preferred profile and convert the final image to it before reducing the file to 8 bits.

Good luck.

Thanks - I want to stick to LR which sets the profile at the same time as the 8 bit reduction in the export process. Not sure if that makes a difference but I'll keep my eye on that.
Alan

[alanmcd]

I will say something else I do notice. And that's the need to leave the Automatic Orange Mask Expansion option ticked. It makes a difference all for the better. And the Unsharp Masking can be strengthened with good results. I can see the result of using this option before I import into LR so it doesn't force any backtracking in my workflow. All other settings I can leave as standard.
thanks for all the help.
Alan

[alanmcd]

At Luminous-Landscape, the ratio on page 12
http://luminous-landscape.com/wp-con...nner-Final.pdf
is given as: 6400ppi scan of 6x7cm negative gives a printable 58x40in
So if all I want is to get 30x20 prints from a 4x5 negative, 1800ppi scans would provide an almost 1 for 1 ratio of input to digital file output ready for printing.
Am I understanding this correctly?
He is assuming a 360ppi printing. My service is asking asking for 254ppi file. I know I don't want to upsample (ie. invent pixels) but is there a problem with 'downsampling' or is there less issue with this. It doesn't have to be an exact one for one does it?

Also: The Luminous paper talks about outputting at 16bit/channel mode. But my printer is asking for 8bit/channel. What is the effect of doing this? The file size of half but does this reduce the quality of the print ?

Thanks
Alan

Let me ask another question for comment on this subject:
If my V800 can deliver 6400ppi without breaching TIF filesize limits, this gives me an 8 x 10 ft print.
Can someone tell me why they would then jump to a drum scan?
It seems that drum scanning would be reserved for billboards or something. And even then, a billboard is viewed from such a long distance that this sort of resolution is totally unnecessary.
So why do we need drum scans?
Alan

[alanmcd]

What I am saying is that, my V800 has a non-interpolated resolution of 6400ppi.
This means that each pixel scanned, placed on a piece of paper at the same distance apart as it was when scanned, will result in an output of 8ft x 10ft (from 4x5" negative).
What megapixel camera would you need to do the same same thing?
Full frame digital - 55 Megapixel?
Am I understanding this paradigm correctly?
Alan